Bidirectional femoral arterial cannula

ABSTRACT

An arterial cannula which includes a diverting side hole which simultaneously perfuses blood to the body and the lower extremity. Two barbs on the cannula exterior position the diverting hole just inside the blood vessel and prevent the back wall of the blood vessel from blocking the diverting hole. A transparent flash chamber on the proximal end of the cannula provides a visual indication of the entrance of the diverting side hole into the blood vessel. When the diverting hole enters the blood vessel, blood immediately fills the flash chamber.

This application is a continuation of application Ser. No. 07/816,874,filed on Jan. 2, 1992, now U.S. Pat. No. 5,171,218.

RELATED CO-PENDING APPLICATIONS

U.S. application Ser. No. 07/600,483, filed on Oct. 19, 1990, titledPERCUTANEOUS TRANSSEPTAL LEFT ATRIAL CANNULATION SYSTEM.

BACKGROUND OF THE INVENTION

In patients experiencing cardiopulmonary failure, a need exists toperfuse blood systemically. A femoral arterial cannula is typically usedto infuse oxygenated blood into the body at the groin. To supply anadequate amount of oxygenated blood, the outer diameter of the cannulaoften occludes the inner diameter of the blood vessel as oxygenatedblood is delivered through the lumen within the cannula. Blood exits thecannula from an opening at the distal end which typically directs bloodtoward the heart of the patient. For patients undergoing long-termcardiopulmonary assistance, the problem of ischemia in the lowerextremity arises since the cannula blocks blood flow to the lower leg. Aneed exists to supply adequate blood flow to the lower leg tissues.

Prior attempts to obviate ischemia caused by arterial cannula occlusionhave been awkward and inadequate. For example, the insertion of anarterial cannula in the aorta to avoid blockage has been suggested.Admittedly, the large diameter of the aorta permits the insertion of alarge cannula without resulting in distal occlusion. However, suchabdominal or thoracic surgery is invasive and more dangerous than theinsertion of a cannula in a femoral artery. These dangers limit invasivetechniques to only the most critically ill patients.

A second cannula can also be used to deliver blood to the lower leg whenthe femoral artery has been occluded by the systemic cannula. Forexample, a Y connector and tube could be inserted proximal to theoccluding cannula and the distal end of the tube fitted with a catheterwhich is inserted into the femoral artery distal to the cannula. Thisalso requires extra hardware and another cannulation.

SUMMARY OF THE INVENTION

A longstanding need exists for a bidirectional femoral arterial cannulawhich will deliver blood in both directions to maintain an adequate flowto the heart as well as in the direction of the lower extremity. Thefemoral arterial cannula of the invention achieves this bidirectionalflow by means of a small diverting hole in the side of the cannula. Thecannula comprises a first tube including a proximal end, a distal tipwith an opening, a diverting side hole, and a barb on the tube exteriorto position the diverting side hole away from the wall of the bloodvessel such that fluid flowing in the first tube exits the distal tipopening in a first direction and exits the diverting side hole in asecond direction. For example, blood is infused in the direction of thelower extremity through the diverting side hole and in the direction ofthe heart and body through the distal tip opening. The tube can beradiopaque to assist in positioning. However, the cannula can beproperly positioned without resorting to fluoroscopic techniques. Acannula wall barb is positioned adjacent the diverting side hole. Thebarb permits the diverting side hole to be properly positioned in theblood vessel so as not to be occluded by the blood vessel wall. Theproximal face of the barb has a steep slope which abuts the inner wallof the blood vessel and prevents the diverting side hole from occluding.The distal facing portion of the barb has a shallow slope whichfacilitates insertion of the barb into the blood vessel percutaneouslyover a guide wire.

The cannula further comprises a hub assembly connected to the proximalend of the first tube. The hub assembly includes a transparent flexiblehub such that when the diverting side hole enters the blood vessel,blood flows into the hub region and provides a visual indication of theentry of the diverting side hole into the blood vessel. The cannulainvention also includes a dilator assembly which is positioned insidethe first tube. The dilator assembly is comprised of a distal end with adiameter which occludes the distal opening of the first tube. Theproximal end of the dilator has a smaller diameter and serves as anobturator which stiffens the dilator assembly. The dilator assembly alsoincludes a dilator hub which inserts into the hub assembly of the firsttube such that a hollow passage is formed between the first and secondtubes which allows blood from the diverting side hole to flow into thetransparent hub assembly region. The dilator assembly further includes aguide wire channel within the second tube which allows for percutaneousinsertion of the bidirectional cannula. As noted previously, the hollowpassage serves as a flash chamber which provides a visual indication ofwhen the diverting side hole enters the blood vessel. The hub assemblyalso includes a flange which can be used to fasten the entire cannulaassembly to the patient's skin.

The addition of a diverting side hole, barb, and a hollow flash chamberfor a visual indication of the entrance of the diverting side holeaffords easy percutaneous insertion and proper placement of thebidirectional cannula in a femoral artery. The cannula is inserted intothe femoral artery until the diverting side hole is inside of the bloodvessel. At this point, blood flows into the transparent passage andflash chamber between the first and second tubes. This provides apositive visual indication to the physician that the diverting side holeis adequately within the blood vessel. The dilator assembly is thenwithdrawn and the proximal end of the cannula attached to a pumpcircuit. Thus, the distal end opening of the cannula provides systemicblood flow to the body while the diverting side hole provides blood flowto the leg. Ischemia and possible necrosis are thus avoided in patientsundergoing extended cardiopulmonary assistance.

The above and other features of the invention including various noveldetails of construction and combinations of parts will now be moreparticularly described with reference to the accompanying drawings andpointed out in the claims. It will be understood that the particulardevice embodying the invention is shown by way of illustration only andnot as a limitation of the invention. The principles and features ofthis invention may be employed in varied and numerous embodimentswithout departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of the cannula of the invention.

FIG. 2 shows a top view of the cannula of the invention,

FIG. 3 illustrates the dilator assembly of the cannula of the invention.

FIG. 4(a) shows the combined cannula and dilator assembly of theinvention.

FIG. 4(b) illustrates the initial placement of the cannula of theinvention in a femoral artery and the operation of the visual indicatorsof the cannula.

FIG. 5 shows a cross-sectional view of the cannula of FIG. 1.

FIG. 6 illustrates a longitudinal cross-sectional view of the cannulawhich encompasses the diverting side hole.

FIG. 7 illustrates a longitudinal cross-sectional view of the cannulawhich encompasses the protuberances.

FIG. 8 illustrates the operation of the cannula of the invention afterthe dilator assembly has been withdrawn and a blood pump attached.

FIG. 9 illustrates the distal flow output of a conventionalunidirectional cannula.

FIG. 10 illustrates the distal flow of the bidirectional cannula of theinvention.

FIG. 11 illustrates the distal pressure output of a conventionalunidirectional cannula.

FIG. 12 illustrates the distal pressure output of a bidirectionalcannula of the cannula.

FIG. 13 illustrates the mixed venous oxygen saturation (SVO₂) of aconventional unidirectional cannula.

FIG. 14 illustrates the mixed venous oxygen saturation (SVO₂) of thebidirectional cannula of the invention.

DETAILED DESCRIPTION OF THE INVENTION

To prevent lower extremity ischemia and resulting tissue necrosis, thecannula of the invention supplies blood to both the body as well as intheopposite direction to the leg. FIG. 1 illustrates the simpleconstruction of the bidirectional femoral arterial cannula. The cannulais comprised ofa radiopaque polyurethane thin wall tube 112, with anouter diameter of 6 mm, which includes a tapered tip 110 with an openingfor supplying blood to the main body of the patient. Tip 110 has aninner diameter of 4 mm andan outer diameter of 5 mm. Tube 112 can betypically 17 French or 14 Frenchin width or other desired sizes as well.FIGS. 5, 6, and 7 illustrate the diverting side hole 38 for supplyingblood to the lower extremity of the patient, and barb 36 for positioningthe cannula diverting side hole within the blood vessel without bloodvessel wall occlusion.

As shown in FIG. 7, barb 36 comprises a distal facing portion 39 with ashallow slope and a proximal facing portion 41 with a steep slope. Theshallow slope of barb portion 39 facilitates insertion of the cannulaintothe artery. The steep slope of barb portion 41 abuts the inner wallof the blood vessel and properly positions the diverting side hole 38.Barb 36 is1 cm in length and 1 mm in height. FIG. 5 illustrates thesymmetrical placement of barbs 36, 5 mm apart, on either side ofdiverting side hole 38, which is located in a depression 43 on theexterior of the wall of cannula 112 and is 2 mm in diameter. As shown inFIG. 6, diverting side hole 38 is slanted with respect to the wall ofcannula 112 and is less likely to be occluded in that position. FIG. 8illustrates the placement of the cannula of the invention in a bloodvessel for long term cardio-pulmonary patient support.

The proximal end 111 of cannula 112 is attached to a polyvinylchloridehub assembly 115. Hub assembly 115 includes a transparent flexible hubin segments 114, 116, and 22. As shown in FIG. 1, barb 36 is located 9cm from tip 110 and 8.5 cm from hub 115. A short hub segment 114 is 1.5cm inlength. Hub segment 116 has a clamp area which is 3.5 cm in lengthextends from flange 118 to hub segment 114. As will be shown below, thetransparent hub provides a visual indication of the entry of thedivertingside hole into the blood vessel. The hub is connected to arigid barbed connector 24 which can be coupled to standard 3/8" tubing.The hub also includes an air bleed inlet 21 with a screwable cap 20which permits adjustment of the opening. Flanges 118 allow the hubassembly to be sewn or clamped onto the patient's skin and preventunwanted movement of the cannula. Flanges 118 are shown in more detailin the top view of FIG. 2.

Dilator assembly 30 of FIG. 3 serves as an obturator or stiffener and isinserted into the interior of the cannula 112 and its associated hubassembly 115. The dilator assembly includes a second polyurethane tube31 with a distal end 28, 9 cm in length, with a first diameter of 4 mmwhichoccludes the first tube distal tip opening. The thickened portionof distalend 28 is 7.5 cm in length. Tapered tip 26 on second tube 31facilitates insertion of the dilator assembly into the first tube of thecannula and dilates the guide wire hole in the vessel for cannulaintroduction. A polypropylene dilator hub with a tapered portion 32seals inside of the rigid barbed connector 24 of hub assembly 115 andouter hub 34 is a handlefor manipulation of the dilator. Portion 47 ofsecond tube 31 is 20.5 cm inlength and has a second diameter of 3 mmwhich is less than the first diameter. Thus, a hollow flash chamber isformed between the first and second tubes which allows blood enteringthe diverting side hole to flow into the hub assembly region. Thisprovides the physician with a visual indication that the diverting sidehole has entered the blood vessel. Onlyblood from the diverting sidehole 38 can enter the flash chamber because the distal end 28 of secondtube 31 occludes the distal end 110 of cannula112. A guide wire 35 canalso be introduced inside of the second tube 31 toguide the insertion ofthe cannula into the blood vessel.

The assembled cannula is shown in FIG. 4(a). FIG. 4(b) illustrates theoperation of the visual indicator during the insertion of the cannulaintothe blood vessel. The diverting side hole 38 is shown resting on thewall of the blood vessel 40. Diverting side hole 38 is 1.5 cm from thethickened portion of distal end 28 of second tube 31. In this position,blood will fill the hollow chamber 37 between first tube 112 and secondtube 31. The blood will flow into the transparent hub region and providethe physician with a visual indication of proper placement. The secondtube 31 of dilator assembly 30 can also be of radiopaque plastic.

FIG. 4(b) also illustrates the placement of the cannula of the inventionusing barb 36 and diverting side hole 38. Skin 42 in the groin region ispierced using a conventional Seldinger needle. Tapered tip 26 on secondtube 31 facilitates the dilation of the blood vessel. Cannula wall 112is threaded into blood vessel 40 until the diverting side hole 38 entersthe blood vessel. As noted previously, blood enters diverting side hole38 andprovides a visual indication in the area of the transparent hub asblood flows into hollow chamber 37. The dilator assembly also serves asan obturator or stiffener to assist in the introduction of the cannula.With air bleed hole 21 open, blood can easily flow into the flashchamber 37. The dilator assembly is then removed and rigid barbconnector 24 is hookedup to standard 3/8" tubing connected to a bloodpump circuit. The hub segment 116 is clamped after the dilatory assemblyis removed. Once connector is attached to the blood pump tubing, theclamp can be removed from hub segment 116.

The bidirectional cannula of the invention provides adequate distalperfusion of the cannulated lower extremity. Thus, extendedcardiopulmonary assistance can be provided with a greatly reduced riskof ischemia to the lower limb. The cannula of the invention can be usedwith any assist circuit. For example, the device could be attached to apercutaneous transseptal left atrial cannulation system. It can also beused for extracorporeal membrane oxygenation where heart function isadequate, but the lungs are failing. Any type of blood pump can be usedwith the cannula of the invention to provide a closed vascular circuit.

FIGS. 9-14 show the experimental data which illustrates the ability ofthe cannula of the invention to maximize pressure, flow, and oxygenationin the cannulated lower extremity. Experiments were performed on 200pound pigs in which a conventional unidirectional cannula was insertedin one femoral artery and the bidirectional cannula of the invention wasinsertedin the other femoral artery. Flow probes and pressure catheterswere positioned distal to the respective cannulae and measurements weretaken over a spectrum of pump flows. Control values are with the pumpturned offand before the cannulae are inserted into the femoral artery.FIG. 9 illustrates the distal flow in an extremity in which aconventional unidirectional cannula has been placed. As can be seen fromFIG. 9, distalflow is non-existent in the lower extremity at all levelsof perfusion. However, as shown in FIG. 10, when the bidirectionalcannula of the invention is used, distal blood flow exceeds controlvalues at full pump flow.

Similar data is produced when distal pressure is measured. For example,FIG. 11 illustrates the distal pressure associated the conventionalunidirectional cannulation. Blood pressure is minimal even at high flowsin the lower extremity. However, when a bidirectional cannula of theinvention is used, blood pressure approaches the control value at fullflow.

Finally, the mixed venous oxygen saturation (SVO₂) was measured as anindex of total limb perfusion, both directly from the cannula and alsofrom native collateral vessels. Low SVO₂ indicates poor perfusionandwith a unidirectional cannula in place it indicates that collateralflow contributes very little to overall limb perfusion. Conversely, highSVO₂ indicates good limb perfusion. The unidirectional cannula in FIG.13 is associated with minimal direct or collateral flow whereas thebidirectional cannula in FIG. 14 produces almost a nominal SVO₂ at highflows.

The bidirectional femoral arterial cannula of the invention providesadequate flow to the limb in cardiopulmonary assistance circuits usedfor long term applications. The barbed diverting side hole and bloodflash chamber are simple to construct and easy to insert into thepatient. Thus,a safe long term method for femoral artery cannulation isprovided with minimal risk to the patient. Positioning can beaccomplished percutaneously without resort to direct surgical exposureor fluoroscopic techniques because of the visual and tactile indicationsprovided to the surgeon by the device.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain, usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. These and all otherequivalents are intended to be encompassed by the following claims.

We claim:
 1. A method of delivering blood through a cannula in apatient, the cannula having a proximal end, a distal end, and adiverting side hole, the method comprising the steps of:inserting thecannula in a blood vessel of the patient, the cannula being inserteduntil the diverting side hole enters the blood vessel; pumping bloodthrough the proximal end of the cannula to the distal end of thecannula; and directing the blood continuously in a first directionthrough the distal end of the cannula and in a second direction oppositeto the first direction through the diverting side hole of the cannula.2. A method according to claim 1, wherein the blood being directed inthe first direction is sent towards the heart of a patient.
 3. A methodaccording to claim 2, wherein the blood being directed in the seconddirection is sent towards the femoral artery of the patient.
 4. A methodof using a bidirectional cannula in a patient, the bidirectional cannulahaving a proximal end, a distal end, and a diverting side hole, themethod comprising the steps of:piercing the skin of the patient with aneedle; inserting the bidirectional cannula through the pierced skininto a blood vessel; threading the bidirectional cannula until thediverting side hole enters the blood vessel; pumping blood through theproximal end of the bidirectional cannula to the distal end of thebidirectional cannula; and directing the blood continuously in a firstdirection through the distal end of the bidirectional cannula and in asecond direction opposite to the first direction through the divertingside hole of the bidirectional cannula.
 5. A method according to claim4, further comprising the step of indicating that the diverting sidehole of the bidirectional cannula has entered the blood vessel.
 6. Amethod according to claim 4, wherein a barb facilitates retention of thecannula in the blood vessel.
 7. A method according to claim 4, whereinthe step of inserting the bidirectional cannula into the blood vesselcomprises using a guidewire.